sync_mailbox() didn't consider MaxSize == 0 to mean "unlimited".
load_config() needs to print a newline in its error messages since
next_arg() kills the newline of the line that was read out of the config
file.
out if new mail arrives while in the process of downloading
noted in BUGS section of man page that if new mail arrives after the initial
message list has been retrieved from the IMAP server, that new mail will not
be fetched until the next invocation of isync.
configuration directives
added `Maildir' configuration command to specify the default location of the
user's mailboxes. If a relative path is used in a `Mailbox' command, this
path is used as a prefix.
